The researchers studied how different forms and ratios of nitrogen affect the metabolism of nitrogen in Grape Plantlets in Vitro. They found that the activity of GS increased with more NH4+—N, reaching the highest level at a 5:5 ratio of NH4+—N to NO3-—N. NR activity increased with more NO3-—N, leading to increased nitrate accumulation. However, as NR activity increased, nitrate accumulation decreased. This shows a significant negative correlation between nitrate accumulation and NR activity.